In recent years, in a display device, such as a thin television represented by a liquid crystal display, aluminum-based alloy wiring material (in some cases, aluminum is hereinafter simply referred to as Al) is widely used as constituent material of the display device, because Al-based alloy wiring material has low specific resistance value and is easy to perform a wiring process.
For example, in an active matrix liquid crystal display, each element is formed of a thin film transistor (hereinafter abbreviated to a TFT) as a switching element, a transparent electrode (in some cases, hereinafter referred to as a transparent electrode layer) made of ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide), and a wiring circuit made of Al-based alloy wiring material (in some cases, hereinafter referred to as a wiring circuit layer). Such an element structure has a portion where the wiring circuit made of Al-based alloy wiring material is bonded to the transparent electrode and a portion where the wiring circuit is bonded to n+-Si (phosphorus-doped semiconductor layer) in the TFT.
When the element described above is formed using Al-based alloy wiring material presently used, refractory metal material, such as molybdenum (Mo) and titanium (Ti), is formed between the wiring circuit and the transparent electrode as a so-called cap layer, considering the effect of aluminum oxide formed in the Al-based alloy wiring material. Similarly, when a semiconductor layer, such as n+-Si, and the wiring circuit are bonded to each other, in order to prevent interdiffusion of Al and Si caused by a thermal operation in the manufacturing process, refractory metal material, such as molybdenum (Mo) and titanium (Ti) as in the cap layer, is interposed between the semiconductor layer and the wiring circuit.
The above element structure will be specifically described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view of an a-Si type TFT for a liquid crystal display. In the TFT structure, an electrode wiring circuit layer 2 made of Al-based alloy wiring material and a cap layer 3 made of Mo, Mo—W or the like, which together form a gate electrode section G, are formed on a glass substrate 1. To protect the gate electrode section G, a SiNx gate insulating film 4 is provided thereon. On the gate insulating film 4 are sequentially deposited an a-Si semiconductor layer 5, a channel protective film layer 6, an n+-Si semiconductor layer 7, the cap layer 3, the electrode wiring circuit layer 2 and the cap layer 3, which are patterned as appropriate to provide a drain electrode section D and a source electrode section S. The drain electrode section D and the source electrode section S are coated with a resin or SiNx insulating film 4′ for planarizing the surface of the element. Furthermore, on the source electrode section S side, a contact hole CH is provided in the insulating layer 4′, where a transparent electrode layer 7′ made of ITO or IZO is formed. When such an electrode wiring circuit layer 2 is made of the Al-based alloy wiring material, the cap layers 3 are interposed between the n+-Si semiconductor layer 7 and the electrode wiring layer 2 as well as between the transparent electrode layer 7′ and the electrode wiring layer 2 in the contact hole CH.
In the element structure shown in FIG. 1, formation of the cap layer made of Mo or the like forces additional cost for material, manufacturing equipment and the like, and its complicated manufacturing process has been pointed out. To address these problems, the applicant has already proposed a technology that allows the cap layers in such a conventional element structure to be eliminated (see Japanese Patent Application Laid-Open No. 2003-89864). Japanese Patent Application Laid-Open No. 2003-89864 discloses Al—C—Ni alloy and Al—C—Ni—Si alloy wiring materials, to which ITO can be directly bonded.